Molecular Adsorption at Particle Surfaces: A PM Toxicity Mediation Mechanism

Abstract

Fine atmospheric particles depositing in the lung present a large adsorbent surface for the adsorption of bronchoalveolar lining fluid (BALF) components, including lung surfactant and its associated proteins. Such adsorption at invading particle surfaces is known to be important in biological particle clearance, and the immunological and toxicological fate of these particles. In the experiments conducted here, it was hypothesized that this is also true for particles of nonbiological origin, and that fine particles with large surface areas would selectively adsorb the opsonizing components of BALF. This work quantifies the adsorption rates (adsorption of compound per unit surface area) of isolated BALF components. Elemental carbon (EC) is a ubiquitous component of fine urban particulate matter (PM2.5), and particular forms of EC are extremely surface active (e.g., activated carbon). EC originates largely from fossil fuel combustion, and vehicles in particular contribute a significant proportion of PM(2.5) EC mass in urban areas. Since the size distribution of EC is submicrometer, industrially produced carbon blacks in the 25-100 nm size range can be used as a surrogate for urban EC, in terms of surface area and chemistry. Three types of carbon black (CB) particles were used. Two were identical in size (25 nm) but different in surface treatment; R330, a CB with a nonoxidized surface, and R400, a CB produced with an oxidized surface. The third particle type, M120, was 75 nm, different in size from R330 and R400, but similar to R330 in surface chemistry, that is, nonoxidized. Particles were first washed and resuspended in phosphate-buffered-saline (PBS, pH 7.0) three times to remove surfactant coatings added during their manufacture. Colloidal suspensions of M120, R330, and R400 particles with decreasing surface areas were then generated and separated into reaction vials. BALF proteins were added spanning physiological concentrations while the dominant phospholipid in surfactant was added at a fixed concentration lower than physiological lung lavage concentrations to ensure the lipid remained in suspension during experimentation ex situ. For dipalmitoylphosphatidylcholine (DPPC) combinations with particles, visible particle agglomeration occurred within 1 h. Marked changes in the size distribution of the immersed particles were observed, compared to a phosphate buffer control. Differences in particle agglomeration and particle settling were observed between M120, R330, and R400. Reduction of DPPC occurred in a surface- and size-dependent manner. This indicates that surface adsorption was responsible for the observed agglomeration and the gross reductions in phospholipid concentrations. Combination of particles with fibrinogen and albumin revealed little agglomeration/precipitation at the protein concentrations chosen. However, surfactant protein (SP-D) was completely eliminated from suspension upon combination with all three-particle types. This reaction between SP-D particles was therefore concluded to be independen...

Fine airborne urban particles (PM2.5) sequester lung surfactant and amino acids from human lung lavage

“…20; Kendall M, unpublished observations) show that particles adsorb DPPC and AAs in vitro, causing marked changes in surface characteristics and particle agglomeration rates. Since surfactant is already known to coat infectious particles and be involved in their clearance via macrophage recognition (40), based on these data here and other works, there is also now evidence to show that this process probably applies to urban fine particles (13,19,20,22).…”

“…Institutional Review Board approval to re-use these diagnostic samples was obtained from New York University as published by Kendall et al (19). Concentrations of SP-A and SP-D in these BAL samples were measured using ELISAs (Yamasa, Japan), and surfactant DPPC was measured according to the methods used in Kendall et al (20). These results are shown in Table 1.…”

“…It is known that surfaces of bacteria are opsonised by lung proteins immediately on deposition. Recent evidence has shown that polymer adsorbants modify PM 2.5 surfaces, and this affects their behaviour in lung fluid (19,20,22). These processes may be important for marking of particles as targets for phagocytosis.…”

The bio-nano-interface in predicting nanoparticle fate and behaviour in living organisms: towards grouping and categorising nanomaterials and ensuring nanosafety by design

“…This lung-surfactant corona was later proposed as an important protective mechanism mediating the health impacts associated with breathing in airborne particles and nanoparticles in urban air [10]. Despite early evidence of particle coronas in the lung identified using newly developed atomic and molecular scale techniques [11], the biological interface remains the least understood aspect about nanoparticles, and classification systems to characterise the outermost layers of the bio-nano interface, i.e., those biological signatures that are available to engage endogenous cellular machinery, are absent.…”

“…-reduced surface energy/reactivity [30] (possibly only temporarily) -depletion of medium components which can result in indirect toxicity effects [8,10,31] -masking targeting or other bio-functional elements? (possibly only temporarily) [32] -altered kinetics (distribution, half-life, degradation, etc.)…”